WI I' ELESS FOR AIRC1' AFT
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An Explanation of the Services Rendered by Wireless Apparatus, and of the Equipment Required for Aeroplanes Flying in Europe. The Marconi Sets • ©scribed
FOR serious air-transport operation on anything but the Shortest routes wireless may be looked upon as necessary. It is required by regulation on public transport machines capable of carrying more than nine persons including the crew.
The pivots of the system are, of course, the ground stations, and in th is country aerodromes well equipped in this respect are at Croydon, Manchester (Barton), Lympne (Kent) and Pulham (Norfolk). Additionally, Heston broadcasts weather reports. The range of these stations depends upon several variable factors, including the quality of any set that is being communicated with, but it may be reckoned that each can transmit, even in bad conditions, over 100 miles, and can receive from stations or aircraft 250 miles awa5 On the Continent wireless aerodromes are separated by seldom above 100 miles throughout the recognized air-travel corridors, and by usually not more than 200 miles in regions away from those corridors.
Croydon has four three-kilowatt transmitters, a direction finder and a beam transmitter. Barton has a new three-kilowatt transmitter with direction finder, also a meteorological office. Lympne and Pulliam stations are equipped for direction finding..
Wireless equipment serves several purposes. It provides for the broadcasting of meteorological information, the exchange between aerodromes of messages concerning aircraft movements, communication between aerodromes and aircraft, the finding of an aeroplane's position and communication of this information to the pilot.
Meteorological information Is usually circulated between aerodromes in the form of fivefigure code messages, but for pilots telephony or plain telegraphy is used. Route-traffic messages between ground stations are transmitted mainly in morse, text records being kept. Simple code is employed to reduce the length of messages. Groundto-aircraft messages can be passed by telegraphy or telephony, but the present tendency is for big air liners to carry a wireless operator and to use the former method, telephony being almost solely confined to small commercial aircraft.
Practically all modern aerodrome wireless stations have direction-finding apparatus, enabling them to read Off the true bearing of any transmitting aircraft. Clearly, two stations in co-operation can " fix " the position of a machine at the intersection (on a large-scale map) of their two bearings. To afford a check on this, the practice is fer three stations to work together, one of them transmitting the result to the aircraft. Under favourable conditions experienced operators can give the position in 1i minute from the time when the pilot asks for it. In fog or darkness the service is invaluable. Pulham and Lympne, keeping a constant watch, B32 work conjunctly with Croydon.
Where such ground services are not available aircraft may carry direction finders and take their own bearings from any two or three suitable transmitting stations. This, however, usually involves carrying an operator.
Croydon has now a directional beam transmitter, enabling aircraft suitably equipped to keep on the path that leads to Croydon. It calls for special apparatus (weighing some 30 lb.) on the aeroplane.
The wireless apparatus in many of the Air Ministry stations in Britain and that on practically all the Imperial Airways ma chines, as well as on nearly 2,000 civil and military aircraft in more than 30 countries is of Marconi manufacture, and we cannot do better than to explain the standard sets made by Marconi's Wireless Telegraph Co., Ltd., Marconi House, Strand, London, W.0.2.
The most generally used set for commercial and other aircraft is the A.D. 6m or Universal type. (There is a lighter set, the A.D.22, for small aeroplanes). Range is difficult to quote dogmatically but, assuming normal atmospheric conditions and modern ground receiving apparatus, the air-to-ground range is about 100-150 miles for telephony, 150-200 miles for interrupted continuous-wave telegraphy and 200-300 miles for continuous-wave telegraphy. It has to be remembered that a 100-mile range is effective when flying between ground stations 200 miles apart. With an electrical capacity of about 0.0003 red. the transmitter and receiver are adjustable to any wavelength between about 550 metres and 1,550 metres.
Usually the windmill-driven dynamo fitted for the A.D. 6m set supplies current also for interior and navigation lights for the aircraft. A modification is the A.D. 6n set, which takes its low-tension current from the lighting.set of the aeroplane and has a small additional windmill for high-tension current ; this naturally makes a saving of about 20 lb., and suits the smaller machines.
Transmitter and receiver normally are mounted in a single case (14 ins. by 20i ins. by 91 ins.) weighing 35i lb. and, thanks to remote control by Bowden cable (weighing 4 lb.) this can be fitted anywhere. Brackets and elastic to provide a mounting insulating the case from shocks weigh 2 lb. 14 oz. The microphone hangs on a leather strap around the pilot's neck, and, with the telephones (preferably incorporated in a special 12-oz, helmet) weigh 34 lb. The telegraph unit (a morse key) weighs 2 lb. 2 oz, and is required only if a separate operator can be carried.
The dynamo with windmill weighs 2g lb. and has a constant-speed device so that, no matter the air speed, the windmill speed remains constant. The non-spillable L.T. battery measures 9i ins, by 41 ins. by 4* ins, and weighs 13 lb.; it can be placed in any convenient position.
The normal aerial is a trailing wire about 200 ft. long with a weight on the end. With its winch it weighs "ii lb. The winch has an automatic brake to regulate the speed of running out, also an automatic stop to prevent it slipping out if the pilot should be interrupted' when winding in. To prevent the aerial fouling the fuselage or tail it is passed out through a tube, called a fairIead (say 2i lb.), which extends perhaps 18 ins. below the fuselage. An aerial ammeter is necessary and weighs 1 lb. Leads for aerial and earth weigh 11 lb.
The weights given above add up to 1011 lb. To this 8 lb. 2 oz. may be added if dual control and intercommunication equipment (allowing pilot and wireless operator to talk to each other) be fitted. For extra batteries, etc., to provide lighting 581 lb. is added.
An important point is that, so far as possible, all metal parts of the aircraft must be electrically bonded and screened. Some machines are bonded in construction as a matter of course. The De Havilland Dragon (all-wood machine) requires an allowance of about 10 lb. for bonding and screening.